Sequential lateral solidification device and method of crystallizing silicon using the same

ABSTRACT

A sequential lateral solidification (SLS) device and a method of crystallizing silicon using the same is disclosed, wherein alignment keys are formed on a substrate with one mask having a plurality of different patterns, and a crystallization process is progressed in parallel to an imaginary line connecting the alignment keys with information for a distance between the mask and the alignment key. The SLS device includes a laser beam generator for irradiating laser beams; a mask having a plurality of areas; a mask stage for moving the mask loaded thereto, to transmit a laser beam through a selective area of the mask; and a substrate stage for moving a substrate loaded thereto, to change portions of the substrate irradiated with the laser beam passing through the mask.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/951,821 filed on Sep. 29, 2004, now U.S. Pat No. 7,115,456 for whichpriority is claimed under 35 U.S.C. § 120 and the present applicationclaims priority of Patent Application No. 10-2003-0096577 filed inRepublic of Korea on Dec. 24, 2003 under 35 U.S.C. § 119. The entirecontents of each of these applications are herein fully incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a method of crystallizing silicon, and moreparticularly, to a sequential lateral solidification (SLS) device and amethod of crystallizing silicon using the same, in which alignment keysare formed on a substrate with one mask having a multiplicity ofdifferent patterns, and crystallization progresses in parallel to animaginary line connecting the alignment keys with information for adistance between the mask and the alignment key.

2. Discussion of the Related Art

As information technologies develop, various displays increase indemand. Recently, many efforts have been made to research and developvarious flat display panels such as a liquid crystal display device(LCD), a plasma display panel (PDP), an electroluminescent display(ELD), a vacuum fluorescent display (VFD), and the like. Some types ofthe flat display panels have already been used in various displaydevices.

LCDs are most widely used because of their beneficial characteristicsand advantages including high quality images, lightweight, thin andcompact size, and low power consumption. LCDs are therefore used as asubstitute for cathode ray tubes (CRTs) for mobile image displaydevices. LCDs have also been developed for use in devices receiving anddisplaying broadcast signals, such as a television, a computer monitor,and the like.

An LCD device generally includes an LCD panel displaying an image and adriving unit for applying driving signals to the LCD panel. The LCDpanel includes first and second glass substrates bonded to each otherand a liquid crystal layer injected between the first and secondsubstrates.

Multiple gate lines are formed on the first glass substrate (TFT arraysubstrate) to be arranged in one direction at fixed intervals, andmultiple data lines are arranged in perpendicular to the gate lines atfixed intervals. Multiple pixel electrodes are formed as a matrix inpixel regions defined by the gate and data lines crossing each other,and thin film transistors are switched by signals of the gate lines totransfer signals of the data lines to the pixel electrodes.

On the second glass substrate (color filter substrate), there is a blackmatrix layer for shielding light from other portions except the pixelregions, an R/G/B (Red/Green/Blue) color filter layer for realizingcolors, and a common electrode for realizing an image.

Spacers maintain the above-described first and second glass substratesat a predetermined interval therebetween, and the substrates are bondedto each other by a sealant having a liquid crystal injection inlet.Liquid crystal is injected between the two glass substrates.

The driving principle of a general LCD device uses the opticalanisotropy and polarization characteristics of liquid crystals. Becausethe structure of liquid crystal is thin and long, the liquid crystalmolecules are aligned to have a specific direction. Based upon dipolemoment, the liquid crystal molecules can have either positive ornegative dielectric anisotropy. Applying an induced electric field tothe liquid crystal controls the direction of the alignment. Therefore,when the alignment of the-liquid crystal molecules is arbitrarilycontrolled, the alignment of the liquid crystal molecules is eventuallyaltered. Subsequently, due to the optical anisotropy of liquid crystals,light rays are refracted in the direction of the alignment of the liquidcrystal molecules to thereby form images.

Recent technologies use an active matrix liquid crystal display (LCD),which is formed of a thin film transistor and pixel electrodes alignedin a matrix and connected to the thin film transistor. This technologyis considered to have excellent high resolution and an ability torepresent animated images.

In an LCD device having a polysilicon semiconductor layer for the thinfilm transistor, it is possible to form the thin film transistor and adriving circuit on the same substrate. Also, there is no requirement toconnect the thin film transistor with the driving circuit, whereby thefabrication process is simplified. In addition, a field effect mobilityof polysilicon is one to two hundred times higher than the field effectmobility of amorphous silicon, thereby obtaining a great stability totemperature and light.

The method of fabricating the polysilicon can be divided into a lowtemperature fabrication process and a high temperature fabricationprocess, depending upon the fabrication temperature.

The high temperature fabrication process requires a temperaturecondition of approximately 1,000° C., which is equal to or higher thanthe temperature for modifying substrates. Because glass substrates havepoor heat-resistance, expensive and brittle quartz substrates havingexcellent heat-resistance should be used. When fabricating a polysiliconthin film by using the high temperature fabrication process, inadequatecrystallization may occur due to high surface roughness and fine crystalgrains, thereby resulting in poor device characteristics, as compared tothe polysilicon formed by the low temperature fabrication process.Therefore, technologies for crystallizing amorphous silicon, which canbe vapor-deposited at a low temperature, to form polysilicon have beenresearched and developed.

The method of depositing amorphous silicon at a low temperature andcrystallizing the deposited amorphous silicon can be categorized into alaser annealing process and a metal induced crystallization process.

The laser annealing process includes irradiating a pulsed laser beamonto a substrate. More specifically, by using the pulsed laser beam, thesolidification and condensation of the substrate can be repeated aboutevery 10 to 100 nanoseconds. The low temperature fabrication process isacknowledged to have the advantage that the damage caused on a lowerinsulating substrate can be minimized.

The related art crystallization method of silicon using the laserannealing method will now be explained in detail.

FIG. 1 illustrates a graph showing the size of amorphous siliconparticles versus laser energy density.

As shown in FIG. 1, the crystallization of the amorphous silicon can bedivided into a first region, a second region, and a third regiondepending upon the intensity of the incident laser energy.

The first region of FIG. 1 is a partial melting region, where theintensity of the laser energy irradiated onto the amorphous siliconlayer melts only the surface of the amorphous silicon layer. Afterirradiation, the surface of the amorphous silicon layer is partiallymelted in the first region, whereby small crystal grains form on thesurface of the amorphous silicon layer after a solidification process.

The second region of FIG. 1 is a near-to-complete melting region, wherethe intensity of the laser energy, being higher than that of the firstregion, almost completely melts the amorphous silicon. After the almostcomplete melting, the remaining nuclei are used as seeds for a crystalgrowth, thereby forming crystal particles with an increased crystalgrowth as compared to the first region. However, the crystal particlesformed in the second region are not uniform. The second region is alsonarrower than the first region.

The third region of FIG. 1 is a complete melting region, whereby laserenergy with an increased intensity, as compared to that of the secondregion, is irradiated to completely melt the amorphous silicon layer.After the complete melting of the amorphous silicon layer, asolidification process is carried out, so as to allow a homogenousnucleation, thereby forming a crystal silicon layer formed of fine anduniform crystal particles.

In this method of fabricating polysilicon, the number of laser beamirradiations and a degree of overlap are controlled so as to formuniform large and rough crystal particles by using the energy density ofthe second region.

However, the interfaces between the multiple polysilicon crystalparticles act as obstacles to the flow of electric current, therebydecreasing the reliability of the thin film transistor device. Inaddition, collision between electrons may occur within the multiplecrystal particles can cause damage to an insulating layer due to thecollision current and deterioration, thereby resulting in productdegradation or defects. In order to resolve such problems, in the methodfor fabricating polysilicon by using a sequential lateral solidification(SLS) method, the crystal growth of the silicon crystal particle occursat an interface between liquid silicon and solid silicon in a directionperpendicular to the interface. The SLS crystallizing method isdisclosed in detail by Robert S. Sposilli, M. A. Crowder, and James S.Im, Mat. Res. Soc. Symp. Proc. Vol. 452, pp. 956-957, 1997.

In the related art SLS method, the amount of laser energy, theirradiation range of the laser beam, and the translation distance arecontrolled, so as to allow a lateral growth of the silicon crystalparticle with a predetermined length, thereby crystallizing theamorphous silicon to a single crystal of 1 μm or more.

The irradiation device used in the related art SLS method concentratesthe laser beam into a small and narrow region, and the amorphous siliconlayer deposited on the substrate therefore cannot be completely changedinto polycrystalline with a single irradiation. Therefore, in order tochange the irradiation position on the substrate, the substrate havingthe amorphous silicon layer deposited thereon is mounted on a stage.Then, after irradiating a predetermined area, the substrate is moved soas to allow an irradiation to be performed on another area, therebycarrying out the irradiation process over the entire surface of thesubstrate.

FIG. 2 illustrates a schematic view of a related art sequential lateralsolidification (SLS) device. Referring to FIG. 2, the related artsequential lateral solidification (SLS) device includes a laser beamgenerator 1, a focusing lens 2 focusing the laser beams discharged fromthe laser beam generator 1, a mask 3 to dividedly irradiate the laserbeam on a substrate 10, and a reduction lens 4 formed below the mask 3to reduce the laser beam passing through the mask 3 to a constant rate.

Generally, the laser beam generator 1 produces light with a wavelengthof about 308 nanometers (nm) using XeCl or a wavelength of 248nanometers (nm) using KrF in an excimer laser. The laser beam generator1 discharges an unmodified laser beam. The discharged laser beam passesthrough an attenuator (not shown), in which the energy level iscontrolled. The laser beam then passes through the focusing lens 2.

The substrate 10 has an amorphous silicon layer deposited thereon, andthe substrate 10 is fixed on an X-Y stage 5 that faces into the mask 3.

In order to crystallize the entire surface of the substrate 10, the X-Ystage 5 is minutely displaced, thereby gradually expanding thecrystallized region.

FIG. 3 shows that the mask 3 includes an open part ‘A’ allowing thelaser beam to pass through, and a closed part ‘B’ blocking the laserbeam to prevent irradiation of the substrate. The width of the open part‘A’ determines the lateral growth length of the grains formed after thefirst exposure.

FIG. 3 shows a plane view of a mask used in a laser irradiation process.FIG. 4 shows a crystallized region formed by a laser beam irradiation byusing a mask of FIG. 3. Referring to FIG. 3, the mask used in the laserirradiation process is formed to have the open part ‘A’ having patternsopened at a first interval (a), and the closed part ‘B’ having patternsclosed at a second interval (b). The open and closed parts alternatesequentially.

The laser irradiation process using the mask will be described asfollows.

First, the mask 3 is placed over the substrate having an amorphoussilicon layer deposited thereon, and then the first laser beam isirradiated onto the substrate. At this time, the irradiated laser beampasses through the multiple open parts ‘A’ of the mask 3, wherebypredetermined portions 22 of the amorphous silicon layer correspondingto the open parts ‘A’ melts and liquefies, as shown in FIG. 4. In thiscase, the intensity of laser energy used herein has a value selectedfrom the complete melting region, so that the silicon layer irradiatedwith the laser completely melts.

At this time, by one laser beam irradiation, the multiple open parts ‘A’of the mask 3 correspond to one unit area 20 of the substrate, to whichthe laser beam irradiated, wherein the unit area 20 has a length ‘L’ anda width ‘S’.

After the laser beam irradiation, silicon grains 24 a and 24 b growlaterally from interfaces 21 a and 21 b between the amorphous siliconregion and the completely melted and liquefied silicon region andtowards the irradiation region. The lateral growth of the silicon grains24 a and 24 b proceeds in a perpendicular direction to the interfaces 21a and 21 b.

In the predetermined portion 22 irradiated with laser for beingcorresponding to the open part ‘A’ of the mask, when the width of thepredetermined portion 22 is narrower than the two times of the growthlength of the silicon grain 24 a, the grains growing inward in aperpendicular direction from both sides of the interface of the siliconregion come into contact with one another at a grain boundary 25,thereby causing the crystal growth to stop.

Subsequently, in order to further grow the silicon grain, the stagebearing the substrate is moved to perform another irradiation process onan area adjacent to the first irradiated area. Thus, another crystalforms with the new crystal being connected to the crystal formed afterthe first exposure. Similarly, crystals laterally form on each side ofthe completely solidified regions. Generally, the crystal growth lengthproduced by the laser irradiation process and connected to the adjacentirradiation part is determined by the width of open part ‘A’ and closedpart ‘B’ of the mask.

FIG. 5 shows a grain boundary overlapped in each channel of devicesformed along one line on a related art crystallization process.

In the related art crystallization process, the crystallization isperformed on the entire surface of the substrate. Accordingly, whencrystallizing the substrate, the stage bearing the substrate moves alongone direction without any alignment key, to change the laser irradiationarea onto the substrate.

However, as shown in FIG. 5, since the crystallization process proceedswithout an index such as the alignment key, the grain boundary 25, whichis the interface of the grains inside the laser irradiated region, isnot rightly perpendicular to the length direction of the device (TFT,30). Also, the number of grain boundaries overlapped in each channel ofthe respective devices is different. For example, one device may haveone grain boundary 25, but another device may have two grain boundaries25. That is, even though the respective devices are provided along oneline, the number of grain boundaries 25 overlapped in each channel(between source electrode S and drain electrode D) of the respectivedevices may differ, and the respective devices will therefore havedifferent mobility characteristics (as the number of grain boundaries 25overlapped in the channel of the device becomes small, the mobilitybecomes rapid). Thus, the respective devices have the differentcharacteristics even though the respective devices are provided alongthe same line.

FIG. 6 shows a plane view of respective areas formed on a substrate.Referring to FIG. 6, a thin film transistor array is formed on asubstrate 50 of an LCD device. The substrate 50 is defined into adisplay area 70 of displaying an image, and a non-display area 60 aroundthe display area 70.

At this time, an amorphous silicon layer is formed on an entire surfaceof the substrate 50. On the display area 70 of the substrate 50,multiple gate and data lines (not shown, formed on other portions exceptpixel regions of the display area) are formed perpendicular to eachother, to define the pixel regions 71. Pixel electrodes are formed inthe respective pixel regions 71. Also, a thin film transistor is formedat a predetermined portion of the pixel region 71, and the thin filmtransistor includes a gate electrode (not shown) protruding from thegate line, a source electrode (not shown) protruding from the data line,and a drain electrode (not shown) formed at a predetermined intervalfrom the source electrode. At this time, a semiconductor layer 75 isformed below the source and drain electrodes, where the semiconductorlayer 75 has a channel between the two electrodes. On the non-displayarea 60, respective driving circuit parts of gate and source drivers 61and 62 are formed to provide signals to the gate and data lines.

However, the crystallization of the amorphous silicon layer formed onthe substrate 50 requires different speeds in the respective areas.Especially, the driving circuit parts 61 and 62, and the thin filmtransistor (device, 75) of the display area 70 require a mobility speedthat is one hundred times higher than those of the remaining portions.Accordingly, in order to decrease the process time and cost for thecrystallization, one can omit the crystallization for the remainingportions which don't require the high mobility speed, and to perform thecrystallization for the driving circuit parts 61 and 62 and the device75 of the display area 70.

To crystallize the device 75 on the substrate of the display area 70, itis necessary to provide an index for laser irradiation areas of thesubstrate. For this, alignment keys are firstly formed on the substrateby a photolithographic process prior to crystallization. In this case,it is necessary to prepare additional masks for the alignment keys,thereby causing the increase of fabrication time and cost forpreparation of the masks.

However, the related art SLS device and the method of crystallizing thesilicon by using the same have the following disadvantages.

In the related art crystallization process, the crystallization isperformed on the entire surface of the substrate without the additionalalignment keys. Accordingly, when the substrate is loaded on the stage,the substrate may slide or turn aside. Alternately, when the mask isloaded to the mask stage, the crystallization process of the substrateprogresses in a non-parallel fashion because the mask is not loaded atthe correct position. However, there is no way to solve these problemsin the related art.

The difficulties presented by the related art are especially acute whenthe gate line, the data line, and the thin film transistor (device) areformed by patterning after crystallization. In this case, the grainboundary formed by the related art crystallization process is notparallel or vertical to the line and device formed in theafter-processing, but is instead slanted thereto. Accordingly, eventhough the respective devices are provided along one line, therespective devices have a different number of grain boundariesoverlapped in the channel, which must be corrected since it may causedegradation of the display quality and reduced speed.

Meanwhile, since the crystallization of the amorphous silicon layerformed on the substrate requires the different speeds in the differentrespective areas, a selective crystallization process has been proposedto decrease the process time and cost for the crystallization. Here, toselectively crystallize the predetermined portion of the substrate, itis necessary to provide alignment keys to index the laser irradiationarea on the substrate. In this case, the process requires both a maskfor forming the alignment key and an additional mask forcrystallization. Also, the process time is delayed due to thereplacement time of the masks for alignment key formation process andcrystallization process, and the cost of the process increases due tothe masks.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a sequential lateralsolidification (SLS) device and a method of crystallizing silicon usingthe same that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a sequential lateralsolidification (SLS) device and a method of crystallizing silicon usingthe same, in which alignment keys are formed on a substrate with onemask having multiple different patterns, and a crystallization processis progressed in parallel to an imaginary line connecting the alignmentkeys with information for a distance between the mask and the alignmentkey.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, asequential lateral solidification (SLS) device includes a laser beamgenerator for irradiating laser beams; a mask having multiple areas suchas an alignment key area and a crystallization area; a mask stage formoving the mask loaded thereto, to transmit laser beam through aselective area of the mask; and a substrate stage for moving a substrateloaded thereto, to change portions of the substrate irradiated withlaser beam passing through the mask.

In the invention, the areas of the mask include at least an alignmentkey area and a crystallization area. The alignment key area includesmultiple minute transmission patterns. The minute transmission patternsare formed at fixed intervals. The substrate is defined as display partincluding multiple pixels and non-display part including a drivingcircuit. Crystallization area of the mask is divided into a first areaand a second area, the first area corresponding to the display part ofthe substrate, and the second area corresponding to the non-display partof the substrate. The first area includes at least one pattern blockhaving multiple transmission parts and non-transmission (blocked) parts.The pattern block has a size corresponding to a semiconductor layer ofone pixel in the substrate. Multiple pattern blocks are formed at fixedintervals. The second area has multiple transmission part and blockedparts. The mask stage is moved to the right and left directions on thesame plane, to be corresponding with the selective area of the mask.

Furthermore, the SLS device includes a tilting mechanism and a levelingmechanism to adjust a minute movement of the mask. The tilting mechanismmoves the mask stage horizontally by rotation. The leveling mechanismmoves the mask stage vertically.

The invention, in part, pertains to an SLS method includes the steps ofpreparing a substrate defined as a display part and a non-display part;forming an amorphous silicon layer on an entire surface of thesubstrate; positioning a mask, defined as an alignment key area and acrystallization area, above the substrate; forming alignment keys bymoving the mask to the alignment key area and irradiating laser beam topredetermined portions of the non-display part; and crystallizing theamorphous silicon layer by moving the mask to the crystallization areaand irradiating laser beam to the display part and a driving circuitpart of the non-display part.

In the invention, the alignment keys are formed at four corners of thenon-display part. The alignment keys are formed by irradiating the laserbeam passing through the alignment key area of the mask at an energydensity suitable for ablation of the amorphous silicon layer of acorresponding portion. The laser beam irradiation using thecrystallization area is performed at an energy density to completelymelt the amorphous silicon layer of a corresponding portion. The laserbeam irradiation using the crystallization area of the mask is performedto obtain the same number of grain boundaries overlapped in each channelof devices provided along one line. A crystallization process directionis parallel with the adjacent alignment keys provided along one line, toobtain the same number of grain boundaries overlapped in each channel ofthe devices provided along one line. The remaining areas that are notselected by the mask are not irradiated, i.e., blocked from irradiationof the laser beam.

Furthermore, the SLS method can include the step of forming a bufferlayer before forming the amorphous silicon layer on the substrate.

The invention, in part, pertains to an SLS method includes the steps ofpreparing a substrate defined as a display part and a non-display part;forming an amorphous silicon layer over an entire surface of thesubstrate; positioning a mask above the substrate, the mask having as analignment key area, a first crystallization area, and a secondcrystallization area; forming alignment keys by moving the mask to thealignment key area and irradiating laser beam to predetermined portionsof the non-display part; crystallizing a portion for a semiconductorlayer of the display part by moving the mask to the firstcrystallization area and irradiating laser beam thereto; andcrystallizing a driving circuit of the non-display part by moving themask to the second crystallization area and irradiating laser beamthereto.

In the invention, the alignment keys are formed at each corners of thenon-display part. The alignment key is formed by irradiating the laserbeam passing through the alignment key area at an energy densitysuitable for ablation of the amorphous silicon layer of a correspondingportion. The laser beam irradiation using the first and secondcrystallization areas is performed at an energy density to completelymelt the amorphous silicon layer of a corresponding portion. Theremaining areas that are not selected by the mask are not irradiated,i.e., blocked from irradiation of the laser beam. The laser beamirradiation using the first crystallization area is performed to obtainthe same number of grain boundaries overlapping in each channel ofdevices provided along one line. A crystallization process direction isparallel with an imaginary line of connecting the adjacent alignmentkeys, to obtain the same number of grain boundaries overlapping in eachchannel of the devices provided along one line. The laser beamirradiation using the second crystallization area is performed byprogressing a crystallization process direction in parallel with animaginary line connecting the adjacent alignment keys. The laser beamirradiation using the second crystallization area is performed in stateof dividing a gate driver formation part and a source driver formationpart. The crystallization process is performed with the same secondcrystallization area of the mask by rotating the mask or the substrateat 90° when the crystallization area is shifted from the gate driverformation part to the source driver formation part.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 shows a graph of the size of amorphous silicon particles versuslaser energy density;

FIG. 2 shows a schematic view of a related art laser irradiation devicefor a general SLS method;

FIG. 3 shows a plane view of a mask used in a laser irradiation process;

FIG. 4 illustrates a crystallized area formed by a first laser beamirradiation with the mask of FIG. 3;

FIG. 5 illustrates a grain boundary overlapped in each channel ofdevices formed along one line on a crystallization process according tothe related art;

FIG. 6 shows a plane view of respective areas formed on a substrate;

FIG. 7 shows a schematic perspective view of an SLS device according tothe invention;

FIG. 8 shows a cross sectional view of a mask stage and a substratestage in an SLS device according to the invention;

FIG. 9 shows a plane view of the mask state of FIG. 8;

FIG. 10 shows a plane view of a mask used for an SLS method according tothe invention;

FIG. 11 shows an expanded view of a pattern formed in a first area ofFIG. 10;

FIG. 12 shows an expanded view of an alignment key formed by an SLSmethod according to the invention;

FIG. 13 shows an expanded view of one pattern formed in a second area ofFIG. 10;

FIG. 14 shows a flow chart of an SLS method according to the invention;

FIG. 15 shows a plane view of respective crystallized areas formed on asubstrate by an SLS method according to the invention; and

FIG. 16A and FIG. 16B illustrate devices provided along one line by anSLS method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 7 shows a schematic perspective view of a sequential lateralsolidification (SLS) device according to the invention. FIG. 8 shows across sectional view of a mask stage and a substrate stage in an SLSdevice according to the invention. FIG. 9 shows a plane view of the maskstage of FIG. 8.

Referring to FIG. 7 to FIG. 9, the inventive SLS device 400 includes alaser beam generator (not shown) irradiating laser beams, a mask 120having multiple areas, a mask stage 310, tilting mechanism 317 andleveling mechanism 315, and a substrate stage 330. At this time, themask 120 having the multiple areas is loaded on the mask stage 310,wherein the mask 120 is moved by the mask stage 310 to transmit laserbeams through a selective area of the mask 120. The tilting mechanism317 and the leveling mechanism 315 minutely move the mask 120. Then, asubstrate 200 is loaded to the substrate stage 330, so that it ispossible to change a laser irradiation portion on the substrate 200 forthe mask 120.

Furthermore, the SLS device 400 according to the invention includes atleast one mirror (‘300’, for reference, 300 a, 300 b, 300 c, 300 d, and300 e of FIG. 8) for changing the laser beam path, a focusing lens (notshown) for focusing the laser beam before transmission to the mask 120,and a projection lens 320 for transmitting the laser beam to acorresponding pattern of the substrate 20 by reducing the laser beamtransmitted to the mask 120.

Also, an optical mechanism is provided over the substrate stage 330,wherein the optical mechanism includes the focusing lens, the projectionlens, the mirror 300, the mask 120, and the mask stage 310. Thus, thesubstrate 200 is loaded on the substrate stage 330, the laser beamirradiates as an adequate pattern onto the corresponding portion of thesubstrate 200, thereby advancing the crystallization process.

At this time, the mask 120 is defined as the multiple areas, anddifferent patterns are defined in the respective areas. For example, themask 120 divides into a first area of alignment key patterns for formingalignment keys 210 a, 210 b, 210 c and 210 d, and a second area forcrystallization of a display part and a driving circuit part.

The mask stage 310 includes an additional tilting mechanism 317 andleveling mechanism 315. As a result, when the mask 120 is loaded on themask stage 310 from an external position, the position of the mask 120is adjusted with the tilting mechanism 317 and leveling mechanism 315.That is, when the mask 120 is not aligned straight in the center, theposition of the mask 120 is adjusted by rotating the tilting mechanism317. If the mask 120 deviates from the center to one side, the positionof the mask 120 is adjusted by backward movement. If the mask 120 is notlevelly loaded, the height of the mask 120 is adjusted with partial orwhole utilization of the leveling mechanism 315 provided at the cornerof the mask stage 310. In this case, it requires accuracy of 1 μm to 5mm. Preferably, the accuracy is 1-100 μm.

After the mask 120 is loaded on the mask stage 310, the mask stage 310is moved to correspond to the respective areas of the mask 120 used tolaser irradiate areas of the substrate, thereby progressing alignmentkey formation and the crystallization process. That is, after completingthe laser irradiation on one laser irradiation area of the substrate,the mask stage 310 is moved at a displacement corresponding to the sizeof one area, to juxtapose the area of the mask 120 with the next laserirradiation area of the substrate.

FIG. 10 shows a plane view of a mask used for an SLS method according tothe invention. FIG. 11 shows an expanded view of a pattern formed in afirst area of FIG. 10. FIG. 12 shows an expanded view of an alignmentkey formed by an SLS method according to the invention.

FIG. 10 shows that the mask used for the inventive SLS method is dividedinto a first area for alignment key formation, a second area forcrystallization of a semiconductor layer of a display part, and a thirdarea for crystallization of a driving circuit part.

As shown in FIG. 11, a pattern 130 for alignment key formation of thefirst area is formed in a shape of ‘

’. Alternately, the pattern 130 may be formed in a shape of ‘

’, ‘

’, ‘

’, ‘

’, ‘

’, ‘

’, ‘

’, ‘+’, ‘

’, ‘X’, ‘Y’, ‘O’, ‘Δ’, ‘Θ’, ‘Φ’, or ‘

’. The invention is not restricted to these patterns, and anyappropriate pattern or combination of patterns can be used.

The pattern 130 for alignment key formation includes multiple minutepatterns 135 provided at fixed intervals. The pattern 130 for alignmentkey formation of the first area allows the formation of alignment keysat the corners of the substrate by laser irradiation. In this case, theenergy density of laser beam is determined at the intensity (or greater)of completely melting an amorphous silicon layer, and of removing theamorphous silicon layer irradiated with laser beam by ablation.

The alignment keys (‘210’ of FIG. 15) are formed by laser irradiationusing the first area of the mask 120, where the alignment keys areformed at or near the four corners of the substrate 200. That is, thelaser irradiation progresses when the substrate stage 300 is moved atall directions to correspond the pattern 130 for alignment key formationof the first area with the four corners of the substrate 200.

FIG. 7 shows the first to fourth alignment keys (210 a, 210 b, 210 c,and 201 d) are formed in a clockwise direction from the upper rightcorner of the substrate 200 to the upper left corner of the substrate200 by using the pattern 130 for alignment key formation of the firstarea.

FIG. 12 shows that when the alignment keys 210 (210 a, 210 b, 210 c, and210 d) are formed on the corners of the substrate 200, each of thealignment keys 210 is formed in a ‘

’-shaped block configuration. Also, since the alignment keys 210 areformed to correspond with the minute patterns 135 of the mask 120, eachof the alignment keys 210 is formed by removing the amorphous siliconlayer according to multiple patterns 215 having a critical dimension(CD) of 1 μm. The invention is not restricted to a 1 μm criticaldimension, and the invention can be used to a critical dimension down toabout 0.1 μm or smaller.

Unlike conventional photolithography that removes or leaves a desiredregion using a photosensitive pattern (photoresist pattern), thealignment keys are patterned according to the following process: ofdepositing a buffer layer (not shown) and the amorphous silicon layer(not shown) over an entire surface of the substrate 200; of volatilizinga predetermined portion of the amorphous silicon layer by increasing theintensity of laser beam irradiation; of forming the multiple patterns215 in intaglio; and of defining the alignment keys 210 a, 210 b, 210 c,and 210 d of ‘

’ shape with the patterns 215.

The alignment key 210 corresponds to the shape of the pattern 130 foralignment key formation at the first area of the mask 120. At this time,the alignment key 210 is formed in a size to reduce the size of thepattern 130 for alignment key formation of the first area of the mask120 by using a reduction ratio of the projection lens 320.

FIG. 13 shows an expanded view of one pattern formed in the second areaof FIG. 10. FIG. 13 shows that the second area of the mask 120 includesone or more pattern blocks 142 (multiple pattern blocks are shown in thedrawings, therefore, the explanation will be described on the basis ofthe state of having multiple patterns blocks) for the semiconductorlayer of the display part. That is, multiple pixel regions 140 areformed corresponding to the display part of the substrate in the secondarea, and the multiple pattern blacks 142 are formed at respectiveportions corresponding to the semiconductor layer of the pixel regions.

Each of the pattern blocks 142 is formed of multiple transmission parts143 and blocked (that is, light occluding) parts 144, wherein thetransmission parts 143 and blocked parts 144 are positioned alternately.

Also, the size of the pattern block 142 is determined in dueconsideration of the reduction ratio (reduced by five times or fourtimes) of the projection lens 320 and the portion for the semiconductorlayer on the substrate 200. That is, the size of the pattern block 142is determined with the value of multiplying the size of the portion forthe semiconductor layer by the reduction ratio. The reduction ratio isnot restricted in the invention. For example, a reduction ratio in therange of two to ten times can be used.

Substantially, the semiconductor layer formed over the substratecorresponds to a portion for a thin film transistor (device), whereinthe channel has a size of 1-100 μm (preferably 10 μm) lengths andwidths. Thus, the device is relatively smaller than a general mask forcrystallization. In contrast, the related art tends to make thetransmission part of the mask for crystallization have the width of 2-10μm in irradiating area (In real mask design dimension, five times theirradiating area. Therefore, the real mask dimension is 10-50 μm), andto make the transmission part have the length of several μm (10-30 mmirradiating area. In real mask design dimension, five times theirradiating area. Therefore, the real mask dimension is 50-150 mm). Onthe other hand, in the invention, each transmission part of the patternblock 142 formed in the second area of the mask has a relatively shortlength of about 10 μm or even less.

Referring to FIG. 10, the third area of the mask 120 includes multipletransmission parts 150 and blocked parts 151, wherein the multipletransmission and block parts 150 and 151 are positioned alternately inthe third area of the mask 120.

The width L of the transmission part 150 may be the same as the width Sof the blocked part 151, or it may be smaller than the width S of theblocked part 151. If the transmission part 150 and the blocked part 151have the same width (L=S), one unit area of the substrate correspondingto a pattern of the third area of the mask is crystallized using twoshots (in this case, the substrate stage is moved to correspond apredetermined portion provided by the blocked part 151 during the firstshot with the transmission part 150 during the second shot), in which itis referred to as a single scan. If the width L of the transmission part150 is smaller than the width S of the blocked part 151, one unit areais crystallized using three or more shots, in which it is referred to asa multi scan.

Meanwhile, the width L of the transmission part 150 is not larger thanthe width S of the blocked part 151, since the mask 120 may be damagedwhen case the mask 120 overheats from the laser beam irradiation.

Hereinafter, an SLS method using the aforementioned SLS device and themask having the multiple areas will be described with reference to theaccompanying drawings.

FIG. 14 shows a flow chart of an SLS method according to the invention.Referring to FIG. 14, in the inventive SLS method, the mask 120 havingthe plurality of areas of the different patterns is prepared (S100) asshown in FIG. 10. For the purpose of explanation, assume that the mask120 has the three areas. Subsequently, the mask 120 is loaded on themask stage 310 of the SLS device (S101). Then, the substrate is loadedon the substrate stage 330 (S102). At this time, the substrate isdefined as the display part of displaying image, and a non-display partaround the display part. Also, the buffer layer and the amorphoussilicon layer are deposited over the substrate in sequence. Then, thesubstrate is fixed to the substrate stage 300 by a fixing mechanism suchas vacuum holes (S103).

Afterwards, the alignment keys are formed at the four corners of thesubstrate by using the first pattern (pattern for alignment keyformation) of the first area on the mask (S104). At this time, thealignment keys are patterned by irradiating the laser beam at an energydensity suitable for ablation of the amorphous silicon layer of thecorresponding portion.

Subsequently, the crystallization direction is controlled to be inparallel with an imaginary line connecting the adjacent alignment keysby information of the distance from the alignment key on the substrate,thereby progressing the crystallization process to the portion for thesemiconductor layer in each pixel region on the substrate (S105). Bycontrolling the crystallization direction to be in parallel with theimaginary line connecting the adjacent alignment keys on the substrate,the crystallization process for the driving circuit part formed in thenon-display part progresses (S106).

During the aforementioned steps S105 and S106, the laser beamirradiation using the first and second areas of the mask proceeds at theenergy density sufficient to completely melt the amorphous silicon layerof the corresponding portion.

When performing the laser beam irradiation using the first and secondareas of the mask, since the devices are provided along one line, it isnecessary to obtain the same number of grain boundaries overlapped ineach channel of the devices provided along one line. When controllingthe number of grain boundaries overlapped in each channel of thedevices, the crystallization process is performed parallel to theimaginary line connecting the adjacent alignment keys on the substrate.The laser beam irradiation using the first and second areas of the maskis performed while controlling the crystallization direction in aparallel direction with the imaginary line of connecting the adjacentalignment keys.

Subsequently, the substrate is unloaded from the substrate stage (S107),and the unloaded substrate stands ready for the next process. During thelaser beam irradiation process using one area of the mask, likealignment key formation (S104) and crystallization (S105 and S106)process, the remaining areas are blocked, i.e., light is not irradiatedonto the remaining areas.

The mask of FIG. 10 is divided into three areas. However, it is alsopossible to use a mask divided into two areas of an alignment key areaand a crystallization area. In this case, the crystallization method ofusing the mask having the two areas uses the same process as thecrystallization method of using the mask of FIG. 10 except that thedisplay part and the non-display area of the substrate are crystallizedusing the crystallization area of the mask.

FIG. 15 shows a plane view of respective crystallized areas formed onthe substrate by the SLS method according to the invention. Referring toFIG. 15, in the laser irradiation process using the SLS method accordingto the invention, the laser irradiation area is divided into threesub-areas, that is, i) the alignment keys 210 a, 210 b, 210 c, and 210d, ii) the display part 220, and iii) the driving circuit part of gatedrivers 230 a and 230 b and source drivers 240 a and 240 b.

The gate drivers 230 a and 230 b and source drivers 240 a and 240 b areformed to have a dual structure at left and right sides or upper andlower sides of the display part 220. Generally, over the substratehaving a thin film transistor array, the driving circuit part may haveone gate driver at one side perpendicular to a gate line, and one sourcedriver at one side perpendicular to a data line. This configurationgives due consideration to the rapid operation of the driving circuitparts.

After forming the alignment keys 210 a, 210 b, 210 c, and 210 d, thecrystallization process is progresses in order of the display part 220and the driving circuit part 230 a, 230 b, 240 a, an 240 b. Alternately,after performing the crystallization for the driving circuit part 230 a,230 b, 240 a, and 240 b, the crystallization for the display part 220may be performed.

As described above, the crystallization process may selectively progressto the portion of the semiconductor layer in the display part 220.Alternately, the crystallization process may progress to the entiresurface of the display part 220 as follows.

The driving circuit part has the gate drivers 230 a and 230 b form in avertical direction, and the source drivers 240 a and 240 form in ahorizontal direction. The crystallization process may be started fromany one of the gate and source drivers.

At this time, after accomplishing the crystallization of the driverprovided at one side of the substrate 200 by irradiating laser with thethird area of the mask 120, the mask stage 310 or the substrate stage330 is rotated by about 90°, whereby a grain boundary having the samedirection forms in each of the devices provided along one line andformed in the drivers.

Meanwhile, the crystallization method using the three areas of the mask120, as shown in FIG. 15, may be used for the substrate having the gatedriver and the source driver defined along one direction, as well as thesubstrate having the gate driver and the source driver defined alongboth directions in the non-display part.

Another SLS method according to another embodiment of the invention willbe described as follows.

Instead of selectively crystallizing a portion of a semiconductor layerin a display part, an entire surface of the display part and a drivingcircuit part crystallizes using the same mask.

In the SLS method according to another embodiment of the invention shownin FIG. 15, a substrate having a display part 220 and a non-display part(remaining portions except the display part) around the display part isprepared. Then, a buffer layer (not shown) is formed over an entiresurface of the substrate 200, and an amorphous silicon layer (not shown)is formed over an entire surface of the buffer layer.

Subsequently, a mask (not shown, having a first area and a third area asin FIG. 10) having alignment key area and crystallization areacorresponds to the substrate 200. Then, a laser beam is irradiated onpredetermined portions of the non-display part through the alignment keyarea of the mask, thereby forming alignment keys. The alignment keys areformed at or near four corners of the non-display part. At this time,the laser beam is irradiated at an energy density suitable for ablationof the corresponding portion of the amorphous silicon layer using thealignment key area of the mask.

After that, the crystallization process progresses by irradiating alaser beam onto the display part and the driving circuit part of thenon-display part through the crystallization area of the mask. The laserbeam irradiation using the crystallization area of the mask uses a laserbeam having an energy density sufficient to completely melt theamorphous silicon layer of the corresponding portion.

On performing the laser beam irradiation using the first and secondareas of the mask, when the devices are provided along one line, itbecomes necessary to obtain the same number of grain boundariesoverlapping in each channel of the devices provided along the one line.When controlling the number of grain boundaries overlapping in eachchannel of the devices, the crystallization process is performed inparallel to an imaginary line of connecting the adjacent alignment keyson the substrate. For the laser beam irradiation process using one areaof the mask, the remaining areas of the mask are blocked, i.e., notirradiated.

FIG. 16A and FIG. 16B illustrate the devices provided along one line byusing the SLS method according to the present invention.

As shown in FIG. 16A and FIG. 16B, the crystallization processprogresses in parallel to the imaginary line 280 connecting the adjacentalignment keys 210 a and 210 b. In the drawings, the imaginary line 280between the adjacent first and second alignment keys 210 a and 210 bruns parallel to the crystallization direction. At this time, a grainboundary forms along the crystallization direction. As a result, thecrystallization process progresses in parallel to the imaginary line 280of the adjacent first and second alignment keys 210 a and 210 b, and thecrystallization direction thus corresponds to the grain boundarydirection.

The semiconductor layer (i.e., the device of the display part, and thedriving circuit part) is patterned by photolithographic process (using apositive or negative photoresist) after crystallization using the firstto fourth alignment keys 210 a, 210 b, 210 c, and 210 d, where thedevices 280 provided along the same line are perpendicular to the grainboundary direction. The number of the grain boundaries overlapping ineach channel of the devices 270 may be one as shown in FIG. 16A, or maybe two as shown in FIG. 16B. However, the invention can be practicedusing any appropriate number of grain boundary overlaps.

Ablation of the amorphous silicon layer forms the alignment key 210before crystallization using the pattern for alignment key formation,formed in the first area of the mask 120. Here, the alignment key servesas the index for a distance from the laser irradiation area of thesubstrate 200, thereby controlling the laser irradiation area(crystallization area). Also, the imaginary line of the adjacentalignment keys corresponds to the grain boundary direction, so that itis possible to realize the same number of grain boundaries overlappingin each channel of the devices, thereby obtaining the uniformcharacteristics in the respective devices.

As discussed above, the SLS device and the SLS method using the samehave the following advantages.

First, a number of different patterns are formed in one mask, so that itis possible to decrease the fabrication cost of the additional mask foralignment key formation before the crystallization process.

By adding the tilting mechanism and the leveling mechanism to the maskstage, the mask is moved along the X-Y-Z-axis, so that it is possible toadjust the position of the mask if the mask is not straight in thecenter (i.e., off center), deviates from the center to one side, or isnot levelly loaded.

Furthermore, the invention achieves the possibility to progress thecrystallization process on the substrate for formation of the grainboundary in parallel with the imaginary line of the adjacent alignmentkeys, thereby obtaining uniform characteristics in the respectivedevices.

By forming the alignment keys before the crystallization process, thealignment keys are used as an index for the distance from the mask, andfor determining parallel alignment with the grain boundary. Also, thealignment keys may be used for the required photolithographic patterningprocess(es) after the crystallization, thereby simplifying thefabrication process.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A sequential lateral solidification (SLS) device comprising: a laserbeam generator; a mask having an alignment key area and acrystallization area; a mask stage, the mask being mounted over the maskstage, the mask stage being moved to transmit the laser beam through aselected area of the mask; and a substrate stage for moving a substrate,to change portions of the substrate irradiated with the laser beampassing through the mask, wherein the substrate has a display partincluding a plurality of pixels and a non-display part including adriving circuit, wherein the crystallization area of the mask is dividedinto a first area and a second area, the first area corresponding to thedisplay part of the substrate, the second area corresponding to thenon-display part of the substrate, and wherein the first area includesat least one pattern block having a plurality of transmission parts andnon-transmission parts, the pattern block having a size corresponding toa semiconductor layer of one pixel in the substrate.
 2. The SLS deviceof claim 1, wherein the alignment key area includes a plurality oftransmission patterns.
 3. The SLS device of claim 2, wherein theplurality of transmission patterns are formed at fixed intervals.
 4. TheSLS device of claim 1, wherein a plurality of said pattern blocks areformed at fixed intervals.
 5. The SLS device of claim 1, wherein thesecond area has a plurality of transmission parts and non-transmissionparts.
 6. The SLS device of claim 1, wherein the mask stage is moved tothe right and left directions on the same plane, to correspond with theselected area of the mask.
 7. The SLS device of claim 1, furthercomprising tilting mechanism and leveling mechanism to adjust a finemovement of the mask.
 8. The SLS device of claim 7, wherein the tiltingmechanism moves the mask stage horizontally by rotation.
 9. The SLSdevice of claim 7, wherein the leveling mechanism moves the mask stagevertically.
 10. A sequential lateral solidification (SLS) mask, whichcomprises: an align key area; and a crystallization area, wherein thecrystallization area of the mask is divided into a first area and asecond area, the first area corresponding to a display part of asubstrate, the second area corresponding to a non-display part of thesubstrate, and wherein the first area includes at least one patternblock having a plurality of transmission parts and non-transmissionparts, and the pattern block has a size corresponding to a semiconductorlayer of one pixel in the substrate.
 11. The mask of claim 10, whereinthe align key are includes a plurality of transmission patterns.
 12. Themask of claim 11, wherein the transmission patterns are formed at fixedintervals.
 13. The mask of claim 10, wherein a plurality of said patternblocks are formed at fixed intervals.
 14. The mask of claim 10, whereinthe second area has a plurality of transmission part andnon-transmission parts.